In general, an X-ray projection image contains many scattered radiation components. This scattered radiation can degrade the accuracy of computed tomography (CT) projection data for three-dimensional imaging using a two-dimensional detector. A two-dimensional detector, like a flat-panel detector used in an X-ray diagnostic apparatus, can use a scattered-radiation-removing grid (e.g., an anti-scatter grid) to suppress scattered radiation. The suppression of scattered radiation can be further improved by post processing the projection data using a scatter-correction algorithm. Scattered radiation correction can be advantageous for extracting low-contrast information, such as when imaging soft tissue.
An X-ray beam in the presence of a scattering object can be modeled as a primary X-ray beam P(x, y) and a scattered X-ray beam S(x, y), wherein the projection data T(x, y) is a composite of these two:T(x,y)=P(x,y)+S(x,y).To correct for the scatter, a kernel-based method can be used. Alternatively, a scatter simulation can be used to compute the scatter based on information of the intervening object responsible for the scatter. Given the simulated scatter, the measured projection data can be corrected by subtracting the simulated scatter, leaving the primary beam for CT reconstruction of an image.
Inefficient scatter simulation and compensation significantly affects imaging quality including poor image contrast, artifact generation, and large errors in CT projection data. In cone-beam CT configured in a wide-beam geometry, scatter correction can become even more important for reconstructing high quality images. Besides hardware-based scatter rejection such as anti-scatter grids and air gaps, approximated-convolution models with experimental parameter calibration is common in current commercial CT. However, for practical clinical application, significant errors (typical 20-40HU) persist when performing scatter correction using approximated-convolution models. Improved methods of correcting scatter in X-ray CT are desired. Further, improvements reducing the computational load and time for scatter correction while maintaining or even improving its accuracy are desired.